One form of steganography is digital watermarking. Digital watermarking systems typically have two primary components: an encoder that embeds a watermark in a host media signal, and a decoder (or reader) that detects and reads the embedded watermark from a signal suspected of containing a watermark. The encoder embeds a watermark by altering the host media signal. The decoding component analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the decoder extracts this information from the detected watermark.
One challenge to the developers of some watermark embedding and reading systems is to ensure that the watermark is detectable even if the watermarked media content is transformed in some fashion. The watermark may be corrupted intentionally, so as to bypass its copy protection or anti-counterfeiting functions, or unintentionally through various transformations (e.g., scaling, rotation, translation, etc.) that result from routine manipulation of the content. In the case of watermarked images, such manipulation of the image may distort the watermark pattern embedded in the image.
A watermark can have multiple components, each having different attributes. To name a few, these attributes may include function, signal intensity, transform domain of watermark definition (e.g., temporal, spatial, frequency, etc.), location or orientation in host signal, redundancy, level of security (e.g., encrypted or scrambled), etc. The components of the watermark may perform the same or different functions. For example, one component may carry a message, while another component may serve to identify the location or orientation of the watermark. Moreover, different messages may be encoded in different temporal or spatial portions of the host signal, such as different locations in an image or different time frames of audio or video. In some cases, the components are provided through separate watermarks.
There are a variety of implementations of an embedder and detector. One embedder performs error correction coding of a binary message, and then combines the binary message with a carrier signal to create a component of a watermark signal. It then combines the watermark signal with a host signal. To facilitate detection, it may also add a detection component to form a composite watermark signal having a message and detection component. The message component may include known or signature bits to facilitate detection, and thus, serves a dual function of identifying the mark and conveying a message. The detection component is designed to identify the orientation of the watermark in the combined signal, but may carry an information signal as well. For example, the signal values at selected locations in the detection component can be altered to encode a message.
One detector implementation estimates an initial orientation of a watermark signal in a host signal, and refines the initial orientation to compute a refined orientation. As part of the process of refining the orientation, this detector computes at least one orientation parameter that increases correlation between the watermark signal and the host signal when the watermark or host signal is adjusted with the refined orientation.
Another detector computes orientation parameter candidates of a watermark signal in different portions of the target signal, and compares the similarity of orientation parameter candidates from the different portions. Based on this comparison, it determines which candidates are more likely to correspond to a valid watermark signal.
Yet another detector estimates orientation of the watermark in a target signal suspected of having a watermark. The detector then uses the orientation to extract a measure of the watermark in the target. It uses the measure of the watermark to assess merits of the estimated orientation. In one implementation, the measure of the watermark is the extent to which message bits read from the target signal match with expected bits. Another measure is the extent to which values of the target signal are consistent with the watermark signal. The measure of the watermark signal provides information about the merits of a given orientation that can be used to find a better estimate of the orientation. Of course other embedder and detectors can be suitably interchanged with some embedding/detecting aspects of the present invention.
Some techniques for embedding and detecting watermarks in media signals are detailed in the assignee's co-pending U.S. patent application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914), U.S. Pat. No. 6,122,403 and PCT patent application PCT/US02/20832. Each of these patent documents is herein incorporated by reference. Of course, artisans know many other suitable watermarking and steganographic encoding techniques.
In related patent application Ser. No. 09/629,401 (now U.S. Pat. No. 6,522,770) assignee disclosed systems and methods for linking from a printed document to an electronic version of the printed document. In one implementation a steganographic signal includes data which is used to determine a memory location at which the electronic version is stored.
According to one aspect of the present invention, we provide documents, systems and methods for creating an electronic version of a printed document. Instead of linking to or finding an electronic version in memory, our systems and methods create a corresponding electronic document itself at least in part by reference to steganographic data included on the printed document. In one implementation we use digital watermark data to help locate areas on a form in which information (e.g., name and address) is to be filled in. The relative locations of the printed document areas are mapped to a generated electronic document. Editable text boxes (or editable areas or fields) are provided at the relative electronic document areas. A user enters information in the editable text boxes or fields.
According to another aspect of the invention, we provide a printed document including steganographic indicia thereon. An example of the printed document is a form to be filled out by a user or applicant, such as a mortgage form. The indicia corresponds to an area on the document to be filled out (e.g., name or social security number, etc.). The indicia preferably provides relative location clues for the area with respect to the document or with respect to other indicia. The indicia also may indicate a field length or expected data input (e.g., numbers vs. letters, etc.). Thus, the indicia provides clues on how best to generate an electronic version corresponding to the printed document.
According to still another aspect of the invention, we provide a system to generate an electronic version of a printed document. The printed document includes steganographic encoding thereon. The encoding including at least a first identifier associated with a first printed document area and a second identifier associated with a second printed document area. The system includes memory; electronic processing circuitry; and a communications bus to facilitate communication between the memory and the electronic processing circuitry. The memory includes software instructions stored therein, the instructions comprising instructions to: generate an electronic version of the printing document including a first electronic document area and a second electronic document area; and relatively position the first electronic document area and the second electronic document area within the electronic version in accordance to a relative positioning of the first printed document area and the second printed document area within the printed document, wherein the relative positioning is determined at least in part from the steganographic encoding.
The foregoing and other features and advantages of the present invention will be even more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.